This invention relates to an apparatus and method for unloading powder from a shipping container. More specifically, the invention covers an apparatus and method for unloading powder coating material from a plastic liner within a box shaped shipping container.
In electrostatic finishing with a powder coating material, the powder is typically delivered to a spray gun from a hopper. For example, the powder can be transferred from a shipping drum to a hopper associated with a powder spray system, as disclosed in U.S. Pat. No. 4,505,623, assigned to Nordson Corporation, the assignee of this invention. The U.S. Pat. No. 4,505,623 patent which is hereby incorporated by reference in its entirety, shows and describes the fluidization and withdrawal of the powder from a cylindrical shipping drum being supported with its axis at a 45 degree angle to vertical. The fluidized powder is then transferred to a feed hopper and pumped from the feed hopper to a spray gun for application to a substrate.
Alternatively to shipping powder in a drum, the original shipping container may also be a smaller container which is typically a square or rectangular cardboard box having an inner plastic liner, i.e., a plastic bag. Normally, the plastic bag is picked up out of the box and the powder is dumped from the plastic bag into the hopper which feeds the spray guns. Attempts have been made to transfer the powder directly from the box to the spray gun hopper or directly to a spray gun by means of a suction tube; however, various difficulties have been experienced with these prior attempts. For example, when the powder level is close to the bottom of the container, the powder tends to gets stuck in the folds of the plastic liner which then must be manually moved about to free the powder and direct it towards the suction tube, or alternatively, the suction tube must be moved to the location of the powder. During this manual procedure, the machine operator has to be careful that powder transfer from the container is not blocked by the plastic liner being sucked against the inlet of the suction tube. The problem of the plastic liner can occur whenever the powder level is near the bottom of the container and therefore the machine, even though it is intended as an automatic transport device, must be manned by an operator to ensure that substantially all of the powder is removed from the container. Moreover, if this type of a device is used to transport powder directly to a spray gun, rather than to an intermediate spray gun hopper, the powder flow through the gun can be very uneven, especially as the powder level is near the bottom of the box, even if the operator is carefully adjusting the bag and suction tube, which causes inferior powder coating.